A). Hormones: Specific molecules made by
special cells and released into thecirculatory system where they travel to target cells
causing a specific response.

Hormone Types:

1). Steroid: fat-soluable molecules
produced from cholesterol. Sex hormones are examples of
these.

2). Hormones derived from amino
acids: most frequently derived from tyrosine are small and
water soluble. Example epinephrine.

3). Peptide
hormones: derived from chains of amino
acids, or peptides. May act as signal molecules in nervous and
endocrine systems.

B). Pheromones:
chemical signals that function between animals of the same species.
Small amounts are used to attract mates, act as territorial markers,
or act as an alarm substance.

C. Local Regulators: chemical messengers
that affect target cells close to their point of secretion.
Neurotransmitters, histamine and interleukins.

D. Prostaglandins: Modified fatty acids
released into extracellular fluid to function as local regulators.
Derived from lipids in the plasma membrane. They work in antagonistic
actions. May induce fever and inflammation.

Mechanism Of Hormone
Action

A. Steroid Hormones and Gene
Expression. These hormones pass through the
target cell and into the nucleus where they bind to a receptor
protein. Here they activate certain genes.

B. Peptide Hormones and Second
Messengers. They are unable to pass through
the plasma membrane and have different methods of action. They attach
to their receptors in the target cell surface and influence activity
within the cell through cytoplasmic intermediates called second
messengers.

The two most important messengers are
cAMP and inositol
triphosphate.

Cyclic AMP: ATP is converted into cAMP
after a series of reactions on the plasma membrane following the
attachment of the hormone to the membrane. cAMP relays the signal
from the membrane to the metabolic machinery of the
cytoplasm.

Inositol Triphosphate: Involves the use of
Ca+2 that regulates cellular protein activity.

Vertebrate Endocrine
System

A.The Hypothalamus and the Pituitary
Gland:

The hypothalamus is a region of the lower brain
that receives information from the peripheral nerves and the brain
and gives off hormones appropriate to environmental
conditions.

Two sets of hormones are
produces:

1). these are produced and stored in the posterior
pituitary

2). releasing factors that regulate the anterior
pituitary.

Pituitary
Gland: an appendage
at the base of the hypothalamus consisting of 2 lobes.

1). Neurohypophysis ( posterior lobe).
releases oxytocin and ADH made by the hypothalamus.

Consists of two lobes located on the ventral
surface of the trachea. Produces T3 (triiodothyrone) and T4
(thyroxine) derived from the amino acid tyrosine. T3 is usually more
reactive than T4. Iodine is the element that is necessary for the
production of these hormones. It also produces and secretes the
material calcitonin which lowers blood calcium by inhibiting the
release from bones. TSH controls the production and release of these
thyroid hormones.

C. Parathyroid Glands:

4 small glands embedded in the thyroid gland.
Secretes Parathormone which regulated the calcium levels in the body.
Vitamin D is needed to function.

D. The Pancreas:

The pancreas produces insulin in the B islets
cells, and glucogon in the A islet cells. Both are controlled by the
sugar level in the blood.

E.The Adrenal
Glands:

Located adjacent to kidneys; each gland is
composed of an outer cortex and an inner medulla. The medulla
produces epinephrine and norepinephrine from the amino acid tyrosine.
Epi is released in times of stress. This is the fight or flight
hormone. Noe- is used primarily to sustain blood pressure. Cortex
produces Glouccorticoids and mineralocorticoids.

F.Gonads:

Produce estrogens, adrogens and progestines.
Controlled by the FSH and LH of the anterior pituitary.

Hormonal control of Calcium
Homeostasis:

A negative feedback system involving 2
antagonistic hormones, calcitonin and parathyroid hormone (PTH),
maintains the concentration of calcium in the blood.

The narrow range is between 9-11 mg.per 100 ml of
blood.

a). A rise of calcium concentration induces the
thyroid gland to secrete calcitonin, which lowers the calcium
concentration by increasing bone deposition and reducing the calcium
uptake in the intestine and the kidneys.

b). When the calcium concentration falls below the
recommended level PTH reverses the effects of calcitonin. PTH is
secreted by the parathyroid gland.

Hormonal control of blood
glucose:

Another negative feedback system involving 2
antagonistic hormones, insulin and glucagon. The ideal glucose level
in humans is 90 mg/100 ml of blood. A rise of glucose in the blood
triggers the beta cells of the pancreas to produce and release
insulin, which acts on the target cells. When blood sugar is too low,
the alpha cells of the pancreas respond to release glucagon which
causes the break down of glycogen in the liver into glucose. This
glucose is released into the blood.